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How does a fruit fly smell?

If you look closely at a fruit fly, you’ll notice that they don’t exactly have a nose between their big, bug eyes. So how is it possible for them to use a sense of “smell” to detect where their next meal might be located?

The answer is in the nanopores located on the cuticle covering sensilla, which are olfactory organs on the antennas of insects. A new study from the RIKEN Center for Biosystems Dynamics Research (BDR) details how these nanopores allow fruit flies to detect chemicals in the air, as well as the gene behind their development.

An insect’s ability to smell allows it to search for food, find mates, and generally react to the environment around it. The nanopores on the cuticle covering the sensilla are believed to work as filters, allowing odorant molecules to enter but keeping larger airborne particles out so the insect can avoid liquid loss.

Through observing developing fruit fly pupa in detail using transmission electron microscopy, researchers found that the cuticular nanopores in fruit flies’ olfactory sensilla originate from a curved ultrathin film formed in the outermost envelope layer of the cuticle. This film is secreted from specialized protrusions in the plasma membrane of the hair-forming (trichogen) cell, and the envelope curvature coincides with plasma membrane undulations associated with structures within the cells.

Microscopic image of fruit fly sensilla. Image Credit: Riken

Continuing further, the research team investigated the genetics behind the formation of pores using next-generation genome sequencing. This led to the discovery of a gene called gore-tex, which is responsible for the formation of the pores.

The gene is a member of the gene family called Osiris, and encodes a protein that is needed for envelope curvature, nanopore formation, and odor receptivity. The Osiris gene family itself is only found in insect genomes, and other genes within this family are expressed in cuticle-secreting cells.

“Our study revealed the elements required for the development of nanopores to allow odor reception, and identified Osiris genes as a platform for investigating the evolution of surface nano-fabrication in insects,” says study leader Shigeo Hayashi. “We hope that studies like this will help us understand how nature builds these fascinating nanostructures that allow living creatures to acquire many specialized functions.”

By Connor Ertz, Staff Writer

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